Electric motor follow-up control system



Oct. 17, 1950 c. J. HlRscH ELECTRIC MOTOR FOLLOW-UP CONTROLv SYSTM Filed'July 11, 1947 o wuuamd INVENToR. CHARLES J. HIRSCH BY M@ ATTORNEYnormal operating conditions.

Patented Oct. 17, i956 y 2,526.23: merano Moron FoLLow-'Ur commonsYs'reM charles J. Hirsch, nougmton, N. y., saigner' to HazeltineResearch, Inc.,

muon-r nunca Chicago, lll., a corpo- Application July 11, 1947, sensiNn. '160,204 n Thls invention relates particularly, to control systemsfor adjusting the magnitude of a iirst electrical efl'ect toward or to 9Claims. (Cl. 31'8-28) to control systems and.

equality with that of a second electrical effect. ,A

Although the invention has wide application. it is particularly usefulin connection with .systems employing radiant energy formeasuring-distancesl electrically and hence will be described in thatenvironment. y l

Some systems heretofore proposed for measuring distances by means of'radiant energy derive in the output circuit of a wave-signal Jreceiverthereof a unidirectional potential having a magnitude which is directlyproportional to'the distance'being measured. To provide a directindication of the measured distance, the distancemeasuring systemincludes a control system having an electrical bridge arrangement bywhich to compare the magnitude of the derived unidirectional potentialwith that of a unidirectional potential of adjustable magnitude.` Whenthe potentials being compared are unequal in magnitude, the bridge isunbalanced. A motor-driven device isenergized in response to anyunbalance of the bridge and is effective, when energized, to adjust themagnitude of the adjustable unidirectional potential to equality withthat of the abovementioned derived unidirectional potential, therebyrestoring the balance of the bridge. The magnitude of the adjustableunidirectional potential thus provides an indication of the measured distance.

A control system of the type described above ordinarily includes a pairof similarly' disposed electron-tube amplifier channels which areconnected between corresponding portions of the bridge arrangement andthe motor of the motor- `driven device. To provide a proper operation ofthe distance-measuring system, it is important that these channels havesubstantially identical gain characteristics at all times and under allOtherwise the accuracy of distance indication is impaired. Equality ofchannel gains is not always easy to realize in practice without frequentreadiustment, particularly over extended periods of operation. Thisisdue, in part, to the fact that the electrical characteristics ofcorresponding electrical compenents of the chann^ls vary unequally overa period oi' time. '1211s is particularly true of the amplifler tubes.Furthermore, should it become necessary to replace one of the amplifiertubes, the previous calibration of the bridge arrangement is no longeraccurate unless the replacement tube has electrical characteristicsexactly correspond- 2 n ing to those of the tube replaced. In practice,this possibility is rather remote.

It is an object of the invention, therefore. to

provide a new and improved control system, lfor adjusting the magnitudeof a rst electrical effect toward equality with that of a secondelectrical effect, which avoids one or more of the abovementioneddisadvantages and limitations of prior such systems.

It is another object of the invention to provide a new and improvedcontrol system lof lche type mentioned which is relatively simple inconstruction yet one characterized by high reliability of operation overrelatively long time intervals without the need of frequent adjustmentthereof.

It is a further object of the invention to provide a new and improvedcontrolvs'vstemv which accomplishes the same end result as theabove-described control system without requiring balanced ,amplifierchannels. v

It is yet another object of the invention to proy vide a new andimprovedcontrol system, for adjusting the magnitude of a first electrical effecttowardequality with that of a second electrical.

effect, .which while providing high accuracy of control is not criticalas to adjustment. y

In accordance with the present invention, a control system comprisesmeans for supplying a first electrical eiect of adjustable magnitude, aninput circuit adapted to4 have applied thereto a second electricaleil'ect, and an input circuit adapted to magnitude of the rst electricaleiect -toward equality with that of the second electrical effect.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawing, and itsscope will be pointed out in the appended claims.

Referring now to the drawing, Fig. 1 is a circuit diagram, partlyschematic, of a radiant-.energy distance-measuring system which includesa conscription thereof is unnecessary. Brieny, however, theinterrogator-responser includes a transmitter for transmittingwave-signal interrogating pulses to a distant object, for example anaircraft I3, the distance of which from the interrogator-responser I2is-to be measured. The air' craft I3 carries a conventional transpondorwhich receives each interrogating pulse and responds thereto bytransmitting a reply wave-signal pulse. Unit I2 also includes a receiverfor receiving the reply wave-signal pulses from the aircraft I2.Interrogator-responser I2 is adapted to develop across the outputterminals thereof a control effect, specifically a unidirectional outputpotential designated en, having a magnitude proportional to theround-trip propagation .time between unit I2 and the aircraft I2 and,hence, la magnitude which is related to the distance therebetween. Theoutput terminals of the interrogatorresponser are connected to a controlsystem I5 embodying the present invention.

'I'he control system I5 includes means for supplying a first electricaleil'ect or potential of adjustable magnitude, this means comprising asource I6 of unidirectional potential'. such as a battery, connected tothe end terminals of a potentiometer I1. The battery I5 is one which iscapable of developing a substantially constant output voltage forapplication to the end terminals of the potentiometer I1. The potentialof adjust.- able magnitude previously mentioned, and designated e1, isdeveloped between the rotary arm Il of the potentiometer and oneterminal thereof. The control system also includes an input circuitadapted to have applied thereto a second electrical effect having amagnitude which may vary over a period of time. `This input circuitcomprises a pair of input terminals 29, 29 which are coupled to theoutput terminals of the interrogator-responser I2 to have appliedthereto the above-mentioned unidirectional potential e2.

The control system I5 also includes an input circuit adapted to haveapplied thereto a third electrical eiect having a magnitude whichvaries, during an operating interval, continuously with time in apredetermined manner over a range of magnitudes including the magnitudesof both the first and the second potentials e1 and en. 'Ihis inputcircuit comprises a pair of terminals 2|,- 2| which are Aadapted to beconnected to a periodic potential generator 22 which may generate apotential of saw-tooth or sinusoidal wave form but which, for purposesof the present description, is assumed herein to generate a sinusoidalpotential. Generator22 thus develops an alternating output potentialhaving' a value which periodically exceeds that of the unidirectionalpotentials el and ez. I'he periodicity of this potential issubstantially greater than the highest expected periodicity of variationof the potential ez.

Controlsystem I5 further includes a control network, responsive to thethree electrical eii'ects and having an operation which is initiatedonly by the potential from the generator 22 each time that the magnitudethereof has a, predetermined the present invention ln relationship withrespect to the magnitude of at least one. of the potentials e: and ez'for adjusting the magnitude of the potential el toward equality withthat of the potential ez. 'I'his means comprises an arrangementdesignated generally by the reference character 25 and includes a pairof diode rectifier *devices 2l and 2.1, the anodes of which areconnectedjitogether and `are also connected to one terminal of thegenerator 22. The cathode oi' the rectiiier device 2l is connectedthrough a resistor 22 to one of the output-terminais of unit I2' whilethe cathode of the rectiiler device 21 is connected through a resistor24 to the rotary arm Il of the potentiometer I1. 'I'he anodes of therectifier devices 29 and 21 are also connected through a resistor 2| tothe anodes of a pair of electron-discharge devices 29 and 39. I'hesedevices are preferably of the gas-nlled type to provide a relativelylarge tlow of energy therethrough, The cathode of the rectifier device26 is connected to the control electrode of the discharge device 29through a coupling condenser 92 and the cathode of the rectiiier device21'is similarlyV connected througha coupling-condenser 93 to the controlelectrode of the discharge device 29. The control electrode of dischargedevice 29 is connected to ground through a unidirectional biasing source25. such as a battery, and a grid resistor 26. 'I'he control electrodeof discharge device 20 is also connected to ground through a battery I1and a grid resistor 99. The cathode of the discharge device 29 isconnected to ground through a direct-current motor 4l which is adaptedto rotate in a predetermined direction. for example in a clockwisedirection, when'energized. The cathode of the discharge device 99 isconnected to ground through a similar directfcurrent motor '4I which isarranged to rotate in the opposite, or counterclockwise, direction whenthe device 30 is conductive. The rotors of the motors 40 and 4I aremechanically coupled to each other, as represented by the broken line,and are coupled to the shaft of the rotary arm I9 of the potentiometerI1.

'Ihe control system also includes means coupled to the potentiometer I1for indicating the magnitude of the potential e: when the potentials e1and e2 are adjusted substantially to equality.A 'I'his means comprisesan indicator 45 including s, suitable xed scale 46 and a pointer 41which is rotatable with respect to the scale and is mechanically coupledto the rotary arm I8 of the potentiometer I 1 as indicated by the brokenline. While the indicator 45 has been represented as separate from thepotentiometer I1, it will be manifest that the two devices may becombined. if desired in a unitary structure.

Considering now the operation of the distancemeasuring system includingthe control system just described, and referring to the curves of Fig.2, a wave-signal interrogating pulse is transmitted by theinterrogator-responser I2 to the aircraft I3 and a reply signal istransmitted or returned thereby. VThis reply signal is intercepted bythe antennasystem I9, Ii and there is developed in the output circuit ofunit i2 a lunidirectional potential ez having a magnitude which isproportional to the distance between unit I2 Yput potential ez of unitI2. It will also be asasaaa'ss sumed that at time to the rectiilerdevices 2l and 21 are in a non-conducting'state due to the respectiveunidirectional potentials en and er applied thereto and that thedischarge devices '29 and I are also nonconductive by virtue oi thehold-oi! biases applied to the' control electrodes thereof from therespective bias sources 35 and 31.

The periodic potential generator 22 applies to the rectiiier devices 26and 21 an output potential.

represented by curve C, which varies sinusoidally over a range ofmagnitudes including the-magnitudes of the unidirectional potentials erand es.

Under the assumedconditions mentioned above, at time tr the magnitude ofthe sinusoidal potential applied to the anode oi the rectifier device 21equals and thereafter exceeds the potential er applied to the cathode ofthis device. The latter thereupon becomes conductive and, during theinterval iti-t5, there is developed across the thel tfI-ta'corrosponding'to the negative' hall, cycle-.of the potential'apliliedto the rectii'lerjievices 2t and 21 by the 'B Ongitr 22. the polarity 0ithis Potential IB- Blloh that thse devices4 are-.hot conduit tiveandthemotors 40 and 4I areV not However, on succeeding 'positive halfWcljof' the potential' of the generator 22, the operation describedabove in connection with the first 'positive half. cycle is repeated,the motor Il. coa timles t0 be intermittently '62161118611 until ithmoved the potentiometer arm lllto a lposition 'the voltage en.V each'positive haltcycle oi the as a control effector energizing potential tothe v direct-current motor 4 I This control effect terminates at time tojust prior to the end at time trof the positive half cycle of thepotential generated -by unit 22. Deiohization of devioe occurs shortlythereafter and it returns to its original nonconductive state.

At time ta the potential applied to the anode of therectifler device 28from the generator 22 is equal to and thereafter exceeds the, biaspofwlierev the voltage el isincieased toa value substantially equal tothel value of the voltage er.;

When. the ,voltage ci is adiusted to equality with potentialapplied tothe control' system il from the generator 22 vmay-,thereafter causeeither one of the discharge devices 28 or I0 to be rendered conductive;so that either thev motor 40 or the motor 4I is energized in the general-manner-previously explained. This causes the, arm 'I8 to be rotated aslight distance 'in a `direction slightly todisturb the equalityv of thepotentials e1 and en. Thus assuming that the discharge device 29 becomesconductive at this time,'it then aplplies a voltage pulse to the motor40, thereby causing the potentiometer arm' Il to be rotatedslightly in acounterclockwise direction. The

voltage e1 then becomes slightly less than the voltage es so that on thenext'succeeding posi- -tive half cycle of the `potential of thegenerator 22, the operation initially Vdescribed' is repeated and themotor 4| operates the potentiometer arm I8 slightly and in a directionwhich tends again to restore equality of the potentials e1 and ci. Thusa series of unidirectional control pulses are applied-to one or theother oi the motors vM and 4I continuously to maintain substantialequality between'tlie magnitudes ofthe potentials ei and e2 as thelatter. may vary from time to time in tential ez applied to the cathodeof this device.

The device 26 thereupon becomes conductive and a potential is developedacross the resistor 23 during the period iis-t4, as represented by curveF. This potential is applied through the coupling condenser 32 to thecontrol electrode of the discharge device 29.` Although the magnitudeoi' the hold-oil bias applied to the input electrodes .of dischargedevice 29 by the battery 35 is exthe voltage drop across the anoderesistor 3| when device 30 becomes conductive further prevents thedischarge device 29 from becoming conductive during the interval ts-t4.Consequently only one of the motors, speciiically the motor II', underthe assumed conditions, is responsive at some time during the intervalto-tv to the control eiiect, represented by curve E of Fig. 2. Motor 4Ithereupon rotates in a clockwise directionland develops an adjusting4force which is applied to the rotary arm I8 of the potentiometer I1.This moves the arm I8 in a direction to in,- crease the potential e1.Shortly after the application of the pulse of energy to the motor 4I, itbegins to rotate at a slower speed and 'tends to come to rest.

accordance with the distance measurement.' It is-apparent from this thatthe indicator I5 oontinuously provides the desired indication of themeasured distance between lthe unit I2 and the aircraft I3. i l

While the `operatior'i has been explained in connection ,with potentialez of fixed magnitude, it will be apparent that a similar operationresults when the'potential e2 varies at any 'periodicity which isapprciably less than the periodicity of the perlodicpotential ofthegenerator 22. Although operatlon of the control system has beendescribed on the assumption `that the generator 22 generates a potentialof sinusoidal Wave form,

it will be manifest that a saw-tooth or otherre-V current potentialgenerator may be employed in lieu thereof so long as thepotential'developed by the generator has a magnitude which varies overarange of magnitudes includingv those of both the potentials er and ez.

It will be 'apparent from the foregoing description that a controlsystem embodying the present invention possesses the important andunique advantages that it is of relatively simple construction, does notrequire the use of amplifier circuits which are critical as toadjustment, does not require reai'justment after the replacement ofelectron tubes having dierent electrical characteristics, and yet aiordsreliable and highly accurate operation over relatively long periods of ytime.

While there has been described what is at present considered to be thepreferred embodiment of` this invention, it will be'obvious to thoseskilled in the art that various changes andY modificationsV may be madetherein without departing from the invention, and it is, therefore,aimed to cover all such changes and modiiications as fall within thetrue spirit and scope of the invention.

What is claimed is:

l. A control system comprising: means for supplying a first electricaleifect of adjustable magnitude; an input circuit adapted to have appliedthereto a second electrical effect; an input circuit adapted to haveapplied thereto only a third electrical effect having a magnitude whichvaries, during an operating interval, continuously with time in apredetermined manner over a range pof magnitudes includingthe magnitudesof both said iirst and said second electrical effects; and acontrolnetwork, responsive to said three electrical effects and having anoperation which is initiated only by said third electrical effect whenthe magnitude of said third electrical effect has a predeterminedrelationship with respect to the magnitude of at least one of said iirstand said second electrical effects for adjusting the-magnitude of saidfirst electrical effect toward equality with that of said secondelectrical effect. l

` 2. A control system comprising: means for supplying a first electricalpotential'of adjustable magnitude; an input circuit Iadapted to haveapplied thereto a second electrical potential; an input circuit adaptedto have applied thereto only a third electrical potential having amagnitude which varies, during an operating interval, continuously withtime in a predetermined manner over a range of magnitudes including themagnitudes of both said i-lrst and said second electrical potentials;and a control network. responsive to said three electrical potentialsand having an operation which is initiated only by said third electricalpotential when the magnitude of said third 'electrical potential has apredetermined relationship with respect to the magnitude of at least oneof said rst and said second electrical potentials for adjusting themagnitude of said rst electrical potential toward equality with that ofsaid second electrical potential.

3. A control system comprising: means for supplying a first electricaleifect of adjustable magnitude; an input circuit adapted to have appliedthereto a second electrical eiect; an input circuit adapted to haveapplied thereto only a third electrical effect having a magnitude whichvaries, during periodic operating intervals, continuously with time overa range of magnitudes including the magnitudes of both said first andsaid second electrical effects; and a control network, responsive tosaid three electrical effects and havingr an operation which isinitiated only by said third electrical eiect each time thatthemagnitude of said third electrical eiect has a predeterminedrelationship with respect to the magnitude of at least one of said firstand said second electrical effects for adjusting the magnitude of saidfirst electrical effect toward equality with that of said secondelectrical effect.

4.1 A control system comprising: means for supplying a first electricaleifect of adjustable magnitude; an input circuit adapted to have appliedthereto a second electrical effect; an input cir-- cuit adapted to haveapplied thereto only a third electrical effect having a magnitude whichvaries sinusoidally over a range of magnitudes including 4the magnitudesof both said iirst and said second electrical eiects; and a controlnetwork. responsive to said three electrical eiects and having anoperation which is initiated only by said third electrical effect whenthe magnitude oi said third electrical effect has apredeterminedrelationship with respectV tothe Vmagnitude of at least one of saidiirst and said second electrical eiects for adjusting the magnitude ofsaid rst electrical effect toward equality with that of said secondelectrical eilect.

5. A control system comprising: means for supplying a first electricaleect of adjustable magnitude; an input circuit adapted to have appliedthereto a second electrical eiiect; an input circuit adapted to haveapplied thereto only a third electrical effect having a magnitude whichvaries, during an operating interval, continuously with time in apredetermined manner over a range of magnitudes including the magnitudesof both said first and said second electrical effects; and a controlnetwork, responsive to said three electrical effects and having anoperation which is initiated only by said third electrical eiect whenthe magnitude of said third electrical eifect exceeds the magnitude ofthe smaller of said ilrst and said second electrical eects for adjustingthe magnitude of said rst electrical effect towardequality with that ofsaid second electrical eiect.

6. A control system comprising: means for supplying a rst electricaleilect of adjustable magnitude; lan. input circuit adapted to haveapplied thereto a second electrical effect having a magnitude which mayvary over a period of time; an input circuit adapted to have appliedthereto only a third electrical eiect having a magnitude which varies,during an operating interval, continuously with time in a predeterminedmanner at a rate substantially greater than that of said secondelectrical eilect and over a vrange of magnitudes including themagnitudes of both said first and said second electrical eilects; and acontrol network, responsive to said three electrical eects and having anoperation which is initiated only by said third electricaleiect when themagnitude of said third electrical eect has a predetermined relationshipwith respect to the magnitude of at least one of said ilrst and saidsecond electrical effects for adjusting the magnitude of said iirstelectrical eilect toward equality with that of said second electricaleffect.

7. A control system comprising: means for supplying a rst electricalleilect o1' adjustable magnitude; an input circuit adapted to haveapplied thereto a second electrical effect having a magnitude which mayvary over a period of time; an input circuit adapted to have appliedthereto only a third electrical eifect having a, magnitude which varies,during periodic operating intervals, continuously with time at aperiodicity substantially greater than the highest periodicity lvariation of said second electrical eiect and over a range of magnitudesincluding the magnitudes of both said rst and said second electricalei'- fects; a control network, responsive to said third electrical e'ectand having an operation which is initiated only by said third electricaleifect for periodically deriving a control eiiect when the magnitude ofsaid third electrical effect has a predetermined relationship withrespect to that of at least one of said rst and said second electricaleffects; and means responsive to said control effect for adjusting themagnitude of said first electrical eifect substantially to equality withthat of said second electrical eiect.

8. A control system comprising: means for eilects; a control networkincluding .at least one of a pair of rectifier devices, responsive tosaid three electrical eiects and having an operation which is initiatedonly by said third electrical effect when the magnitude thereof has apredetermined relationship with respect to that of at least one of saidrst and said second -electrical effects for periodically deriving acontrol effect; and means including at least one 0f a pair ofelectron-dischargeV devices responsive to said control eiect forderiving an adjusting force and for applying said adjusting force tosaid rst-mentioned means to adjust the magnitude of said firstelectrical eiect substantially to equality with that of said secondelectrical eiect.

9. A control system comprising: means including a. potentiometer forsupplying a rst electrical effect of adjustable magnitude; an input 30`2,435,955

vary over a period of time; an input circuit adapted to have appliedthereto only a third electrical etect having a magnitude which varies,during periodic operating intervals, continuously with time at aperiodicity substantially greater than the highest periodicity ofvariation of said second electrical eiect and over a range of magnitudesincluding the magnitudes of both said irst and said second electricaleffects; a control network, responsive to said three electrical effectsand having an operation which is initiated only 4by said thirdelectrical eiect when the magnitude thereof has a predeterminedrelationship with respect to that of at least one of said ilrst and saidsecond electrical effects for periodically REFERENCES CITED Thefollowing references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date Hartig i Feb. 17, 1948 Isserstedti. Feb. 17, 194s

